The invention relates to a device for supplying measured quantities of alumina to the break in the crust of an electrolytic cell. The said device features a moving transporting facility which is situated in a stationary channel and is connected to a power drive facility and an alumina silo.
Devices for providing a continuous supply of alumina to electrolytic cells for fused salt electrolysis of alumina have been known for about 50 years. These devices resulted from the knowledge that alumina has to be fed to the bath in quantities corresponding to the amount of aluminum deposited at the cathode. It was therefore an early idea to combine the facility for feeding alumina to the cell with one for supplying measured quantities thereof. In the known devices the alumina is fed by means of a feeding screw and compressed air, a feeding screw and piston compressor, or by a scattering method. Other known methods of feeding alumina is by means of gravity feeders and fluidizing channels.
With the known feeding devices the place of feeding alumina to the cell varies between feeding through the anodes themselves, having the facility directly on the anode (in particularly with Soderberg pots), or having the alumina fed at some other place of choice on the cell.
The disadvantage of the feeding devices known up to now lies in particular in the complexity of construction, and in the cost of manufacturing such devices. Screw feed units in particular require a continuously turning motor which is electrically driven. This represents a considerable risk factor when used on electrolytic cells.
Feeding screws must have a certain (even if minimal) distance between them and the surrounding walls in order to have freedom to turn. Alumina can gather in these spaces, and, especially if it is the kind which is not completely dry, this can lead to sticking and therefore considerable interruptions in production.
Furthermore, adjusting the amount to be fed to the cell is difficult and inaccurate with a screw feed device as the spaces between any two threads of the screw do not fill up uniformly. This can therefore often result in too little alumina being fed to the cell and consequently more frequent anode effects, or too much being fed, which leads to uneconomic operation of the cell.
It is therefore an object of the invention to develop a device for feeding measured quantities of alumina to the break in the crust on an electrolytic cell, whereby the disadvantages of the known feeding devices are avoided.